Method for marking metal articles



Dec. 14, 1965 E. F. MILLER, JR 3,222,752

METHOD FOR MARKING METAL ARTICLES Filed Feb. 25, 1963 INVENTOR. EARLE F MILLER, JR.

United States Patent C) 3,222,752 METHUD F05. MARKHNG METAL ARTECLE Earle F. Miller, l ra, $03 S. Star, El Dorado, Kane. Fit-led Feb. 25, 1963, Ser. No. Zilfl' 4 Ciairns. (Cl. 29-%) This invention relates to a method of marking metal articles of or for manufacture for identification purposes.

Certain metal articles of or for manufacture cannot be satisfactorily marked for identification purposes because subsequent manufacturing processes such as heat treating, etching, machining, grinding, grit blasting, peening, painting, weathering, and the like will remove or conceal any marking. Accordingly, the identification indicia will be lost. Moreover, high stress metal parts of critical limitation cannot be punched, cut, scratched, or otherwise structurally marred because this will destroy the usefulness of the part. Also, the use of tags or marking with ink or paint may not be considered practical. The tags could get interchanged or lost and usually must eventually be removed; and the ink or paint markings will become obliterated in subsequent processing or use.

It is an important requirement, particularly in the manufacture of aircraft, that certain articles of manufacture be machined from large forgings. It is also a requirement that every test specimen meet stated specifications of critical physical properties. It is therefore necessary to see that these properties are being maintained. Once the identification indicia has been effaced the part cannot be traced to the originating vendor or other responsible source. In Government procurement, it is particularly desirable that vendors assign identification numbers to vended parts for test specimen identification purposes.

There is, therefore, a need for a new method of satis factorily permanently marking parts, especially parts having critical strength requirements that cannot be permanently marked by cutting, scratching, or stamping. There is also a need for a new method of causing an article of manufacture to be permanently marked with identification indicia so that its origin can be traced. The identification indicia is needed to identify vendors, heat treat lots, associated test specimens, and the like.

One of the objects of this invention is the provision of a novel method of marking an article of or for manufacture for future identification in such a manner that the marking is permanent and is not destroyed or obliterated by manufacturing processes such as heat treating, etching, light machining, grit blasting, peening, and/ or painting, that the article is not damaged, and/or that the marking can be done quickly with minimum cost.

Another object of this invention is the provision of a novel method of marking an article of or for manufacture consonant with the requirements set forth in the preceding object including the step of peening the article for marking the same by forming impressions, preferably with the aid of stencils, of identifying indicia, such as code symbols, letters, and/ or numbers.

Another object of this invention is the provision of a novel method of marking, with identifying indicia, articles of or for manufacture by shot peening with the use of stencils having indicia, such as symbols, letters, and/or numbers formed therein, the indicia preferably being of rounded shape and not having any sharp corners so that when this novel marking method is used no damage, such as the creation of high stress areas, will occur to the article.

Further objects and advantages of the invention will be apparent to those skilled in the art to which it pertains from the following description.

The figure in the drawing is a perspective view of a metal article having an identification indicia being shot peened thereon through a stencil.

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It is to be understood that this invention is capable of being otherwise embodied and of being practiced and carried out in various ways. It is to be further understood that the terminology employed herein is for the purpose of description and there is no intention to herein limit the invention beyond the requirements of the prior art.

Referring to the drawing, reference numeral 10 indicates generally an article of or for manufacture that is desired to be marked by the process embodying this invention. A template 11 is placed over the article 10 and a suitable shot impelling or peening apparatus 12 that can be carried in an operators hand 13 is employed for the peening operation. The peening apparatus 12 is connected to a compressed gas hose 18 which provides a selected gas pressure. Preferably, the hose provides air at a pressure of 60 p.s.i.g. or greater. Peening is accomplished by discrete blasting particles or material such as beads, balls, shot, out wire, or pellets. The template 11 is provided with an identification indicia 11a formed therein. This indicia comprises code symbols, letters, or numbers, as desired, it being a condition of this illustration that this indicia not include any sharp corners that would create high stress conditions or areas in the article 10 by this marking process. The stencil is preferably made of metal such as brass or steel for long life. However if desired, the stencil can be made of regular shot peen masking tape or a thick nonmetal such as Nylon, Teflon, rubber, or elastomer. Stencils made from electrical tape may be used for marking parts on flat or curved surfaces.

In order to control the disposition of the blasting particles 14, the peening is preferably done in some kind of an enclosure, such as a cabinet 15. The cabinet 15 has a window 16 with heavy gauntlets 17 for an operators hands. The cabinet 15 has facilities for the recovery and reuse of the blasting particles 14 and also provides safety protection to personnel.

It is preferred that glass shot of suitable size, such as 0.046 inch diameter glass balls or beads, be used for marking critical high stress parts particularly of the kind required in aircraft landing gear and wing terminal forgings. It has been found that round glass shot gives better indentations because other type shot may be of multiple facets, or so easily deformed as not to leave the desired surface condition. The more the peening particles deviate from roundness the greater the surface roughness for a given peening condition. The roughness produced by peening is a function of the diameter and depth of the indentations produced by the peening partic es.

It is understood that stencil size, shot size, and/or peening compositions, and depth of peening penetration of the part may vary depending upon each specific application. Basic criteria are surface area available for marking, condition of surface area, surface hardness of the part, and the expected penetration depth of any subsequent etching, machining, or peening operation. The peening process must be capable of producing symbols on the part that are in sharp relief relative to the surrounding part surface when peening through a stencil. The distinctness and clarity of detail or outline produced by peening through a stencil is directly related to the surface roughness of the part.

It has been found that for clear definition of the identification indicia on the article surface, the peening material is best directed at an angle against the stenciling surface. It is also desirable, in order to obtain the necessary sharpness of relief, to play the peening material from the gun around the perimeter of the stencil cutout 11a until 'lrademarks of Dupont, Wilmington, Delaware.

the entire exposed surface is uniformly and completely peened to the desired depth. Exposure time greater than that required for 100% coverage will reduce the roughness. Dwell time, however, should be of sufiicient length to insure desired depth of penetration. Usually dwell time is determined empirically and is a function of the air pressure, peening material size, weight, and composition, and the distance between the peening gun 12 and the stencil 11. Properly applied identification indicia will be visible after all subsequent manufacturing operations, such as light etchings, machining, shot peening, heat treating, and/or painting. When a subsequent ope-ration involves coldworking or a surface preparation by shOt peening or grit blasting in the area of the part surface slated to be marked by this process, the particles selected for marking the part should preferably be selected so that the roughness of the marking will not be overshadowed by the roughness of the shot peening or grit blasting, particularly on a part made of a light colored metal. This can best be accomplished by selecting a marking particle size that is equal to or greater than the size of the shot to be used for peening of the overall part. When the marking particle is the same size as the peening shot, the impelling intensity of the marking particle is preferably higher than the intensity specified for shot peening or grit blasting. When the marking particle size is less than the peening shot size, the blasting intensity of the marking particle need not exceed that specified for shot peening or grit blasting. A blasting intensity of the marking particles must be selected that will not distort the part being marked. The maximum allowable blasting intensity will depend on the thickness of the part, the type of alloy, and hardness of the alloy.

It is generally required that a relatively flat area of sufficient size to accommodate the desired identification indicia must be available on the part to be identified. This area must be selected so as not to interfere with the operation or other requirements of the part. Also, it is desired that this area be in a prominent place easily observed for future reference purposes. It is also advantageous that the identification process be applied at the predetermined surface of the article or part as soon as possible so that proper identification control can be had. It is understood, however, that after installation of a part in its final assembly or environment, the accessibility and lighting conditions of the marked area will affect visual recognition of the identification indicia. The identification indicia can be lifted from a part by placing a sheet of relatively thin light colored paper over the identification indicia and lightly stroking over the paper with the lead of a pencil. Thus a most effective means of positive identification is obtained and a perfect record can be maintained. Suitable indicia, such as symbols of Arabic numerals and the English alphabet, have been conceived for use in this process and are disclosed in co-pending design patent applications of Earle F. Miller, Jr., et al., Serial No. 73,688, filed February 25, 1963, now Design Patent No. 200,078, and Serial No. 73,701, filed February 25, 1963, now Design Patent No. 200,079; both issued January 12, 1965. However, it is to be understood that other indicia can be used as desired or found suitable.

It will be understood that this invention can be modified to adapt it to various circumstances and conditions, and it is accordingly desired to comprehend within the purview of this invention such modifications as may be considered to fall within the scope of the appended claims.

What is claimed is:

1. A method of permanently marking a critical high stress metal article of or for manufacture with intelligence indicia comprising symbols, numerals or letters, including the step of peening the critical high stress metal article with discrete spherical peening particles through a stencil bearing intelligence indicia having rounded and smooth filleted indicia free of sharp corners so that the critical high stress metal article when stenciled with the indicia will be free of high stress concentration areas, and said discrete spherical peening particles being of a size and impelled with compressed gas at a sufficient pressure to give the stenciled indicia the desired depth, surface smoothness and uniformity in the critical high stress metal article that will visibly contrast with the unstenciled surface of the critical high stress metal article.

2. A method of permanently marking a critical high stress metal article of or for manufacture with intelligence indicia comprising symbols, numerals or letters, including the step of peening the metal article with discrete peening particles comprising glass balls having an approximate diameter of five hundredths of an inch through a stencil bearing intelligence indicia having rounded and smooth filleted indicia free of sharp corners so that the metal article when peened with the indicia will have a low stress indicia configuration free of high stress areas, said discrete peening particles being impelled with compressed gas at a predetermined pressure of at least 60 psi. until the stenciled indicia is at a predetermined depth and uniformity in the metal article, and said discrete peening articles being directed at an oblique angle against the surface of the article being marked in such a manner that said peened indicia will have a low stress smooth filleted edge rimming the indicia configuration free of high stress areas.

3. A method of permanently marking a critical high stress metal article of or for manufacture with intelligence indicia comprising symbols, numerals or letters, including the step of peening the metal article with discrete peening articles directed obliquely through a stencil bearing intelligence indicia having rounded and smooth filleted indicia free of sharp corners so that the metal article when peened with the indicia will be free of high stress areas, said discrete peening particles and said gas pressure being selected to provide a peened surface roughness that suitably contrasts with the unstenciled surface of the metal article, and said discrete peening particles being impelled with compressed gas at a predetermined pressure until the stenciled indicia is at a predetermined depth and uniformity in the metal article.

4. A method as set forth in claim 3, wherein said discrete peening particles are 0.046 inch diameter glass balls impelled by a compressed gas at a minimum pressure of 60 p.s.i.a.

References Cited by the Examiner UNITED STATES PATENTS 3/1936 Morgan 1179 OTHER REFERENCES RICHARD H. EANES, JR., Primary Examiner. 

1. A METHOD OF PERMANENTLY MARKING A CRITICAL HIGH STRESS METAL ARTICLE OF OR FOR MANUFACTURE WITH INTELLIGENCE INDICIA COMPRISING SYMBOLS, NUMERALS OR LETTERS, INCLUDING THE STEP OF PEENING THE CRITCAL HIGH STRESS METAL ARTICLE WITH DISCRETE SPHERICAL PEENING PARTICLES THROUGH A STENCIL BEARING INTELLIGENCE INDICIA HAVING ROUNDED AND SMOOTH FILLETED INDICIA FREE OF SHARP CORNERS SO THAT THE CRITICAL HIGH STRESS METAL ARTICLE WHEN STENCILED WITH THE INDICIA WILL BE FREE OF HIGH STRESS CONCENTRATION AREAS, AND SAID DISCRETE SPHERICAL PEENING PARTICLES BEING OF A SIZE AND IMPELLED WITH COMPRESSED GAS AT A SUFFICIENT PRESSURE TO GIVE THE STENCILED INDICIA THE DESIRED DEPTH, SURFACE SMOOTHNESS AND UNIFORMITY IN THE CRITICAL HIGH STRESS METAL ARTICLE THAT WILL VISIBLY CONTRAST WITH THE UNSTENCILED SURFACE OF THE CRITICAL HIGH STRESS METAL ARTICLE. 